A control relay is used in the automotive industry to restrict and regulate the flow of electricity to various electrical parts inside the automobile. They allow a small circuit to control a higher flow circuit using an electromagnet to control the flow of electricity inside the circuit. They are usually labeled and identified on the fuse box panel.
A control relay helps to prevent wires from overloading and overheating. Overheated wires can spark a fire. They do not prevent volt spikes. If a relay switch stops working for some reason, it is practical to test it. This is very applicable in automobiles, as one switch can control a large flow of electricity. As a result, if the switch shuts down, a fair portion of the automobile will shut down.
Many retailers will not accept returns on electronic parts. It is not too difficult to test relays to ensure that they actually do need replacement before purchasing the part. The first part of identifying a bad relay is performing a visual inspection. A bad one will usually have burned contacts. Sometimes the contacts can become so corroded that they are green in color and do not allow any electricity to flow through them.
In some cases, the cover is very difficult or impossible to remove. The part can be swapped with another connected part to see if the circuit is working or not. If the swapped part works, but the original part does not, then a bad relay can be identified.
The only way to truly test a relay to identify the extent of damage is with a meter. There are a few steps involved in testing this way. There are some general guidelines, and the first steps are usually the same.
An automobile control relay vary in size from the 3-pin to 5-pin types. The 4-pin type is generally used throughout the automobile. If it shuts down and testing is needed, it is important to note the size of the relay. It also helps to identify the pins themselves if they are not labeled. Pins can be identified using an ohmmeter.
Testing can be done with a test light, which is recommended because it draws a current through the switch. Testing can also be done with a voltmeter or an ohmmeter. Testing relays with built-in clamping diodes requires a special procedure. These are polarity sensitive: placing B+ to the wrong pin, or backwards, while testing will reverse the diode polarity. This damages it and destroys its protective quality. This is a concern when testing with both voltmeters and ohmmeters.